1. Field of the Invention
The present invention relates to synthetic filaments having a trilobal or tetralobal cross-sectional shape with substantial convex curves, connected by cusps, along the contour of each lobe. The filaments are especially suitable for making carpets which exhibit low glitter, high bulk, and resistance to fibrillation.
2. Description of the Related Art
Fibers, or filaments, having trilobal and tetralobal cross-sections have been widely used for carpet yarns due to their bulk and covering power advantages over fibers having round or ribbon cross-sections. However, conventional trilobal and tetralobal filaments contain lobes having cross-sectional contours which are generally flat, or only slightly concave or convex. As a result, at certain viewing angles, a specular reflection from these fiber surfaces creates a "glittering" and frosty appearance on the carpet yarns which is objectionable to many carpet buyers.
By the term, "glittering", it is meant the specks of light perceived on yarns when intense light is directed at the yarn. This is due to minute fiber sections acting as mirrors or reflecting prisms. The term, "glittering", should not be confused with the term, "luster". By the term, "luster", it is meant the overall glow of the fiber from reflected light. Fibers are commonly referred to as having a bright or dull luster, but may or may not be free of glitter.
Examples of trilobal and tetralobal fibers having a high degree of glitter, or sparkle, are respectively disclosed by Bankar et al., U.S. Pat. No. 4,492,731, and McKinney, U.S. Pat. No. 3,109,220. When such high glitter fibers are dyed or pigmented, specular reflection gives the impression that the fiber color is lighter than its true color. Thus, additional dye or pigment is required to compensate for the reflective properties of the fibers. Furthermore, specular reflection is especially visible in highly crimped yarns which are needed to confer high bulk and covering power on premium grade carpets.
Those skilled in the art have proposed many different ways to reduce specular reflection from the surface of fibers.
For example, filaments having round cross-sections typically exhibit less specular reflection and have a more subdued luster. However, due to bulk and covering power deficiencies, these fibers are not widely chosen for use in carpets.
It is also known to add various delusterants, such as titanium dioxide, to the polymer spinning dopes when preparing trilobal and tetralobal fibers. Although these fibers show a more subdued luster, they also have an undesirable chalky appearance.
Shah, U.S. Pat. No. 3,994,122, discloses a crimped polyamide staple filament mixture comprising 40-60% by weight of trilobal filaments having a modification ratio within the range of 1.6-1.9, and 40-60% by weight of trilobal filaments having a modification ratio within the range of 2.2-2.5. The filaments provide high bulk, high luster without undesirable sparkle and glitter, and improved resistance to soiling.
Craig, U.S. Pat. No. 2,959,839, discloses making ribbon-like filaments from a series of unconnected round spinneret orifices arranged in a zig-zag pattern. The filaments have corrugated surfaces and exhibit reduced glittering.
Although such conventional filaments, as described above, have been somewhat effective in reducing specular reflection in carpets, there is a need for trilobal and tetralobal filaments which exhibit even lower glitter, while also providing high bulk. The filaments of the present invention demonstrate an improved combination of low glitter, high bulk, and resistance to fibrillation in the finished carpet.